In the aftermath of the First World War, Britain and France famously created the modern Middle East by carving up what had been the Ottoman Empire. The borders of new states such as Iraq and Syria were determined in keeping with British and French needs and interests. The wishes of local inhabitants were largely ignored.

Now, for the first time in over 90 years, the whole postwar settlement in the region is coming unstuck. External frontiers are no longer the impassable barriers they were until recently, while internal dividing lines are becoming as complicated to cross as international frontiers.

In Syria, the government no longer controls many crossing points into Turkey and Iraq. Syrian rebels advance and retreat without hindrance across their country’s international borders, while Shia and Sunni fighters from Lebanon increasingly fight on opposing sides in Syria. The Israelis bomb Syria at will. Of course, the movements of guerrilla bands in the midst of a civil war do not necessarily mean that the state is finally disintegrating. But the permeability of its borders suggests that whoever comes out as the winner of the Syrian civil war will rule a weak state scarcely capable of defending itself.

The same process is at work in Iraq. The so-called trigger line dividing Kurdish-controlled territory in the north from the rest of Iraq is more and more like a frontier defended on both sides by armed force. Baghdad infuriated the Kurds last year by setting up the Dijla (Tigris) Operations Command, which threatened to enforce central military control over areas disputed between Kurds and Arabs.

Dividing lines got more complicated in Iraq after the Hawaijah massacre on 23 April left at least 44 Sunni Arab protesters dead. This came after four months of massive but peaceful Sunni protests against discrimination and persecution. The result of this ever-deeper rift between the Sunni and the Shia-dominated government in Baghdad is that Iraqi troops in Sunni-majority areas behave like an occupation army. At night, they abandon isolated outposts so they can concentrate forces in defensible positions. Iraqi government control in the northern half of the country is becoming ever more tenuous.

Does it really matter to the rest of the world who fights whom in the impoverished country towns of the Syrian interior or in the plains and mountains of Kurdistan? The lesson of the last few thousand years is that it matters a great deal. The region between Syria’s Mediterranean coast and the western frontier of Iran has traditionally been a zone where empires collide. Maps of the area are littered with the names of battlefields where Romans fought against Parthians, Ottomans against Safavids, and British against Turks.

It is interesting but chilling to see the carelessness with which the British and French divided up this area under the Sykes-Picot Agreement of 1916. The British were to control the provinces of Baghdad and Basra and have influence further north. The French were to hold south-east Turkey and northern Syria and the province of Mosul, believed to contain oil. It turned out, however, that British generosity over Mosul was due to Britain having promised eastern Turkey to Tsarist Russia and thinking it would be useful to have a French cordon sanitaire between themselves and the Russian army.

Sykes-Picot reflected wartime priorities and was never implemented as such. The British promise to give Mosul to France became void with the Bolshevik revolution in 1917 and the Bolsheviks’ unsporting publication of Russia’s secret agreements with its former French and British allies. But in negotiations in 1918-19 leading up to the Treaty of Versailles, only the most perfunctory attention was given to the long-term effect of the distribution of the spoils.

Discussing Mesopotamia and Palestine with David Lloyd George, Georges Clemenceau, the French Prime Minister, who was not very interested in the Middle East, said: “Tell me what you want.” Lloyd George: “I want Mosul.” Clemenceau: “You shall have it. Anything else?” Lloyd George: “Yes, I want Jerusalem too.” Clemenceau agreed with alacrity to this as well, though he warned there might be trouble over Mosul, which even then was suspected to contain oil.

Those negotiations have a fascination because so many of the issues supposedly settled then are still in dispute. Worse, agreements reached then laid the basis for so many future disputes and wars that still continue, or are yet to come. Arguments made at that time are still being made.

Not surprisingly, the leaders of the 30 million Kurds are the most jubilant at the discrediting of agreements of which they, along with the Palestinians, were to be the greatest victims. After being divided between Iraq, Turkey, Iran and Syria, they sense their moment has finally come. In Iraq, they enjoy autonomy close to independence, and in Syria they have seized control of their own towns and villages. In Turkey, as the PKK Turkish Kurd guerrillas begin to trek back to the Qandil mountains in northern Iraq under a peace deal, the Kurds have shown that, in 30 years of war, the Turkish state has failed to crush them.

But as the 20th century settlement of the Middle East collapses, the outcome is unlikely to be peace and prosperity. It is easy to see what is wrong with the governments in present-day Iraq and Syria, but not what would replace them. Look at the almost unanimous applause among foreign politicians and media at the fall of Colonel Gaddafi in 2011, then look at Libya now, its government permanently besieged or on the run from militia gunmen.

If President Bashar al-Assad did fall in Syria, who would replace him? Does anybody really think that peace would automatically follow? Is it not far more likely that there would be continued and even intensified war, as happened in Iraq after the fall of Saddam Hussein in 2003? The Syrian rebels and their supporters downplay the similarities between the crises in Iraq and Syria, but they have ominous similarities. Saddam may have been unpopular in Iraq, but those who supported him or worked for him could not be excluded from power and turned into second-class citizens without a fight.

US, British and French recipes for Syria’s future seem as fraught with potential for disaster as their plans in 1916 or 2003. In saying that Assad can play no role in a future Syrian government, the US Secretary of State, John Kerry, speaks of the leader of a government that has still only lost one provincial capital to the rebels. Such terms can only be imposed on the defeated or those near defeat. This will only happen in Syria if Western powers intervene militarily on behalf of the insurgents, as they did in Libya, but the long-term results might be equally dismal.